Diamond has excellent semiconductor characteristics, in addition to its excellent mechanical, chemical and thermal characteristics, and accordingly, diamond is attracting attention as a semiconductor device material. Particularly, diamond has a band gap of about 5.5 eV at a room temperature, and has high dielectric breakdown characteristics, and accordingly, diamond is expected as a power device. Further, diamond has robust crystalline characteristics, and thereby diamond is expected also as an environment resistant device to be used particularly under a severe environment such as at a high temperature and under radiation.
Recently, diamond power devices have actively been developed. For example, reports relating to a schottky barrier diode having a schottky junction, a device with a PIN structure, a device with a combination of a schottky junction and a PN junction, and so on have been made.
However, phosphorus (P) that is an n-type impurity is hardly introduced into a {100} plane of a diamond crystal. For the reason, it is difficult that n-type diamond on the {100} plane is made to have a low resistance, and in addition, it is difficult to control for making an n-type layer with a low concentration which is used as a drift layer or the like.
Hitherto, reports have been made for forming an n-type layer with a low resistance, but an n-type layer with a lot of defects has been formed, and thereby a good pn junction has not been formed. For the reason, it is expected that a diamond semiconductor device has a good pn junction, and has a high withstand voltage and a low resistance.